Photosynthesis Gas Exchange System with Internal CO2 Directly Measured

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  • BOYER John S.
    College of Earth, Ocean and Environment and College of Agriculture and Natural Resources, University of Delaware This work was supported by a USDA Grant #93-37306-9578 from the NRI-CGP to JSB
  • KAWAMITSU Yoshinobu
    College of Agriculture, University of the Ryukyus

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Abstract

In this study, a leaf gas exchange system was constructed and tested over an extended range of external CO2 concentrations (ca) while the concentration inside the leaves (ci) was directly and continuously determined. For ca, an infrared analyzer was used to compare ca with a reference gas at concentrations as high as 50,000 μmol•mol−1. For ci, a glass cup sealed to the abaxial leaf surface equilibrated with internal CO2, and the gas was circulated to another infrared analyzer. When stomata were open in the light in a sunflower (Helanthus annuus L.) leaf, ci was about 275 μmol•mol−1 in ca of 400 μmol•mol−1. If stomata closed in the dark, ci increased until it exceeded ca but in the light the reverse occurred and ci decreased to only 60 μmol•mol−1. When ca increased in light, stomata began to close but ci could be increased to 50,000 μmol•mol−1, overcoming the closure. But inward CO2 diffusion was further inhibited by water vapor diffusing outward. The inhibition agreed with theoretical calculations of von Caemmerer and Farquhar (1981). The system expanded the CO2 concentrations at which CO2 fixation could be measured while avoiding complications from calculating ci when stomata close.

Journal

  • Environment Control in Biology

    Environment Control in Biology 49 (4), 193-207, 2011

    Japanese Society of Agricultural, Biological and Environmental Engineers and Scientists

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